Orphanin FQ/Nociceptin (OFQ/N) interacts with Opioid Receptor Like-1 receptor (ORL1) in different parts of the central nervous system (CNS) and plays a role in both the production (supraspinally) and alleviation (spinally) of pain. This difference in response by OFQ/N may be due to its action on different forms of ORL1 or due to different circuitry pathways for ORL1 in the CNS. SH-SY5Yand BE(2)-C human neuroblastoma cell lines endogenously express ORL1 receptors. These cell lines represent important model systems for ORL1 receptor multiplicity and understanding the nature of OFQ/N activation of ORL1 isoforms in the CNS; these issues will be investigated in three specific aims mentioned. Aim 1: To determine the contribution of the primary structure of the ORL1 receptor to its different pharmacological profiles in SH-SY5Y and BE(2)-C cell lines. Aim 2: To determine the mechanism of the apparent mu-opioid-ORL1 receptor interactions in BE(2)-C cell lines. Aim 3: To determine if native and novel ORL1 and mu-opioid receptors are localized in human brain and spinal cord tissues. Techniques that will be used to solve the above aims include sequencing, cloning and expression of ORL1 receptor, SDS-page, immunoblotting, fluorescent peptide binding and immunocytochemistry. Understanding the role of receptor isoforms and the contribution of other opioid receptor systems in OFQ/N analgesia will help in designing new analgesic agents that can block hyperalgesia elicited by endogenous OFQ/N, but utilize its analgesic properties.